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Chemistry 5 - Formulae, Equations and Amounts of Substance > Doing Titrations > Flashcards

Doing Titrations Flashcards

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1
Q

what is a titration

A
  • a practical method of measuring the volumes of two solutions that react together
  • and then using that information to calculate the concentration of one of the solutions
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2
Q

what is a base that is soluble in water called

A

an alkali

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3
Q

why do we use indicators in a titration which change the colour of the solution depending on whether it is acidic, alkali or neutral

A
  • because all the acids and alkalis as well as the products made from them reacting are colourless
  • meaning that you would need an indicator to visually know when the reaction is complete
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4
Q

what is the summarised method of a titration

A
  • add the acid to the alkali until the equivalence point of the titration and end point of the indicator is reached
  • record the lowest part of the meniscus
  • record the titre
  • repeat until concordant titres are obtained
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5
Q

what is a meniscus

A

the lowest part of the solution level in the burette if a concave shape is formed

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6
Q

what are the common apparatus used in a titration

A
  • a conical flask
  • a burette and stand
  • a pipette and pipette filler
  • a white tile
  • a small funnel
  • a wash bottle containing deionised water
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7
Q

what is the very first step of a titration

A
  • rinse the conical flask with deionised water

- place on a white tile

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8
Q

what is the second step of a titration

A
  • use a pipette filler to rinse the pipette with deionised water
  • then fill with sodium hydroxide solution
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9
Q

what do you do after the pipette has been rinsed

A

you use the pipette to transfer a known volume of sodium hydroxide solution into a conical flask

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10
Q

what is then added into the conical flask

A

2 to 3 drops of an indicator (methyl orange or phenolphthalein)

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11
Q

what is then done to the burette after this

A
  • it is rinsed with deionised water
  • and filled with the acid solution
  • to be set up in the stand above the conical flask
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12
Q

after you record the reading on the burette taking the meniscus into consideration, what is the important part of this titration

A
  • adding the acid solution into the conical flask until it just changes colour
  • in which you would then record the reading on the burette again
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13
Q

what is the final step in order to get concordant titres

A
  • empty the conical flask and rinse it with deionised water

- then repeat the experiment again

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14
Q

why do you use a white tile

A
  • it provides a constant white background

- for the indicator colour change to be seen more easily

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15
Q

why do only add 2 to 3 drops of indicator for every titration

A
  • many acid or base indicators are weak acids
  • so they have an impact on the end point of the titration
  • this would cause inaccuracies if different volumes of indicator were used in different titrations for the same solutions
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16
Q

why do you fill the burette so that the gap between the tap and the tip is fiilled

A
  • when the tap is turned on some of the solution in the burette will fill this gap
  • meaning your initial reading is essentially wrong
  • because some the of the solution will fill this gap and not enter the conical flask
17
Q

how can you increase the accuracy of the reading of the meniscus

A
  • by recording the burette to the nearest half a small division (0.05cm^3)
  • using a light background to see the bottom of the meniscus
18
Q

what do you do to decrease the chance of overshooting the end point

A
  • add the acid solution from the burette steadily at first
  • then much more slowly as the end point is approached
  • then drop by drop when very close while swirling the flask
19
Q

why do you stop adding solution form the burette just when the indicator changes colour

A
  • to increase the accuracy of the titre
  • adding any more solution does not change the colour any further
  • but the accuracy will decrease
20
Q

why should you repeat to obtain concordant results

A
  • to increase the accuracy of your final calculated reading

- they should be within 0.2cm^3 of each other

21
Q

why do you rinse the pipette and burette with deionised water and the solution to be used whereas the conical flask is only rinsed with deionised water

A
  • because there would be an unknown amount of solution being titrated
  • which would induce an error
22
Q

what is the titre

A

the volume added from the burette during the titration

23
Q

what is the end point and equivalence point and why should they coincide with each other

A
  • the equivalence point is when the solutions completely neutralise each other or when the reaction is complete
  • the end point is when the indicator just changes colour
  • they should more or less happen at the same time or be as close as possible for your data to be accurate
24
Q

what are concordant titres

A
  • titres that are close together when you have repeated the titration
  • usually within 0.2cm^3 of each other
25
Q

what should the colour of methyl orange be in an acid and alkali

A
  • it should be red in an acid

- and yellow in an alkali

26
Q

what should the colour of phenolphthalein be in an acid and alkali

A
  • it should be colourless in an acid

- and pink in an alkali

27
Q

what are the acid-base combinations for methyl orange

A
  • strong acid with weak base

- strong acid with strong base

28
Q

what are the acid-base combinations of phenolphthalein

A
  • weak acid with strong base

- strong acid with strong base

29
Q

what are the typical examples of strong acids

A
  • hydrochloric acid

- nitric acid

30
Q

what are typical examples of strong bases

A
  • sodium hydroxide

- potassium hydroxide

31
Q

what are the common weak acids and bases

A
  • the common weak base is ammonia

- the common weak acid is ethanoic acid

Chemistry 5 - Formulae, Equations and Amounts of Substance (15 decks)

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